  q 退出
  ! [command] 测试命令
  
  
NAME
    man - format and display the on-line manual pages
    格式化显示在线手册
    
SYNOPSIS
       man  [-acdfFhkKtwW]  [--path]  [-m system] [-p string] [-C config_file] [-M pathlist] [-P pager] [-B browser] [-H htmlpager] [-S section_list] [section]
       name ...

DESCRIPTION
       man formats and displays the on-line manual pages.
       If you specify section, man only looks in that section of the manual.
       name is normally the name  of the  manual  page,  which is typically the name of a command, function, or file.
       
       However, if name contains a slash (/) then man interprets it as a file
       specification, so that you can do man ./foo.5 or even man /cd/foo/bar.1.gz.
       See below for a description of where man looks for the manual page files.

MANUAL SECTIONS
       The standard sections of the manual include:
       1      User Commands  用户命令

       2      System Calls   系统呼叫

       3      C Library Functions  C库方法

       4      Devices and Special Files  设备和驱动文件

       5      File Formats and Conventions  文件格式和约定

       6      Games et. Al.  游戏等 (??)

       7      Miscellanea    杂记 (??)

       8      System Administration tools and Deamons  系统管理工具和守护进程 (??)

       Distributions customize the manual section to their specifics, which often include additional sections.
  